Opening of the panel discussion. Roger Holmber

FIRST INTERNATIONAL SYMPOSIUM ON

ROCK FRAGMENTATION BY BLASTING LULEA, SWEDEN, AUGUST 2 2 - 2 6 , 1983

S-WAVE RADIAL FRACTURING JOINT INITIATED FRACTURING

/

OPENING OF WEAKNESS PLANES

FLEXURAL RUPTURE FRACTURING

REFLECTED" ^PRESSURE-WAVEFRACTURING

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First International Symposium on ROCK FRAGMENTATION BY BLASTING Lulea, Sweden, August 23-26,1983

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Volume No. 3.

Printed by TECE-tryck AB, LuleS, Sweden ISBN 91-7260-851-x

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First International Symposium on ROCK FRAGMENTATION BY BLASTING

August 23 - 26, 1983 Lule& University of Technology

edited by Roger Holmberg

Agne Rustan

SPONSORS National Swedish Board for Technical Development (STU) Swedish Detonic Research Foundation (SveDeFo) Swedish Mining Research Foundation Lulea University of Technology

PURPOSE This symposium is the first international convocation of scientists and engineers committed to open discussion and continuous information exchange on current progress, on-going research and engineering innovation in the field of fragmentation by blasting. By organizing this kind of forum the hope is that the future research can be focused on those areas where most efforts are needed.

Published by LULEA UNIVERSITY OF TECHNOLOGY Division of Mining and Rock Excavation S-951 87 Lulea, Sweden, 1983

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ORGANIZING COMMITTEE: Per-Anders Persson, chairman, Nitro Nobel AB Agne Rustan, program, Lulea University of Technology Roger Holmberg, papers, Swedish Detonic Research Foundation Bengt Aaro, tours, Swedish Mining Research Foundation Ingemar Marklund, LKAB Ebbe Pehrsson, Boliden Mineral AB Lennart Ottosson, Atlas Copco MCT AB Gunnar Almgren, Lulea University of Technology

This publication can be ordered from: LULEA UNIVERSITY OF TECHNOLOGY CENTEK 5-951 87 LULEA SWEDEN

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PREFACE

The First International Symposium on Rock Fragmentation by Blasting was held in Lulea, Sweden, at the Lulea University "of Technology during August 23-26, 1983. It attracted 157 participants, and 18 accompanying persons from the 23 following .countries; Australia Austria Brazil Canada China Costa Rica Finland France Great Britain India Israel Italy Nigeria Norway Spain South Africa Soviet Union Sweden Switzerland Thailand USA Zimbabwe West-Germany.

' '•

'

16 2 1 5 11 1 5 2 6 1 1 2 1 5 . 2 2 < 1 67 1 1 21 1 2

The symposium was held under economical guarantee from The National Swedish Board for Technical Development and the Lulea University of Technology. The arrangements in Lulea were made under the responsibility of the Swedish Detonic Research Foundation, The Swedish Mining Research Foundation and Lulea University of Technology. Before the symposium mine tours were arranged to the Research Mine at Luossavaara, to LKAB in Kiruna and Malmberget and to the open pit mine "Aitik" belonging to the Boliden Mineral Co. The scientific program included 51 pape'rs where 48 papers are published in volume 1 and 2. Three papers are published in this third volume which also includes opening speech, key—notes and discussions. Preparations for a Second International Symposium on Rock Fragmentation by Blasting are underway.

Dr Per—Anders Persson Chairman of the Organizing Committee

Roger Holmberg Head of papers

Agne Rustan Head of program

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Electronic publication by Daniel Johansson 2015-06-25 after permission by Editors-in-chief Agne Rustan and Roger Holmberg

Electronic publication bySymposium Daniel Johansson 2015-06-25 after permission by Editors-in-chief Participants of the First International on Rock Fragmentation by Blasting in Lulea, Sweden, August, 1983.

Agne Rustan and Roger Holmberg

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VOLUME No. 1 - 3 TABLE OF CONTENTS Page Volume

Welcome to Lulea University of Technology. Vice Chancellor Dr Torbjorn Hedberg

815

3

Opening of the Symposium and Introduction. Dr Pen-Anders Persson, Chairman of the organizing committe

-817

3

Key-note. Fragmentation - a Review. Disintegration of solids. Ulf Langefors, Sweden

819

3

Gaps in the Field of Fragmentation by Blasting and some Thoughts about Future Research and Development. Agne Rustan, Sweden

8.27

3

Blasting Experiments in the Luossavaara Research Mine. Torbjorn Naartijarvi, Sweden

839 • ' 3

Discussion

855

KEY-NOTE SESSION

Session 1. IMPORTANT PARAMETERS FOR ROCK FRAGMENTATION Chairman: C.M. Lownds, vice chairman: Agne Rustan A Study of Bench Blasting in Rhyoporphyry at a Reduced Scale and the Statistical Analysis of the Regularity for Fragmentation Distribution. Ma Bailing et al, China

857

Production Drilling with high Accuracy. Lars Hermansson, Sweden

789

Energy in Fragmentation. Per—Anders Persson, Sweden

777

Discussion 1

873

Measurements and Predictions of Borehole Pressure Variations in Model Blasting Systems. F.O. Otuo'nye et al, USA

7

The Effect of Charge Cavity Ratio on Rock Breaking. Zhu Rui—Geng et al, China.

21

The Influence of Controllable Blast Parameters on Fragmentation and Mining Costs. T.N. Hagan, Australia

31

Discussion 2

875

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Page

Volume

The Role of Stress Waves in Explosively Induced Bulk Rock Motion. J.N. Edl, USA.

53

1

Effect of Explosive Properties, Rock Type and Delays on Fragmentation in Large Model Blasts. O.R. Bergmann, USA.

71

1

On the Applicability of the Tensile Strength as an Index to Rock Fragmentation. Kenneth Maki, Sweden

79

1

Dynamic Photoelastic Studies on Delayed Pre-split Blasting. K.R.Y. Simha et al, USA

g7

1

The Influence from Specific Charge, Geometric Scale and Physical Properties of Homogenous Rock on Fragmentation. Agne Rustan et al, Sweden

-|-J5

1

Regulations of the Process of Hard Rocks Fragmentation by Blasting. K.A. Dolgov, USSR.

143

1

Discussion 3

876

3

Spallation, Break-Up and Separation of Layers by Oblique Stress-Wave Interaction. H.P. Rossmanith et al, Austria

149

1

Theoretical Research and Modelling of Directed Crack Propagation in Borehole Blasting. A.L. Isakov et al, USSR.

169

1

Model Studies on Explosively Driven Cracks under Confining In-situ Stresses. K.R.Y. Simha et al, USA

183

1

New Methods of Measuring Fracture Toughness on Rock Cores. F. Ouchterlony et al, Sweden

199

1

Discussion 4

883

3

Session 2. THEORY OF FRACTURING AND CRACK PROPAGATION Chairman: W.L. Fourney, vice chairman: Agne Rustan

Session 3. INSTRUMENTAL SYSTEMS FOR EVALUATION OF FRAGMENTATION Chairman: Dinis da Gama, vice chairman: Gunnar Almgren Rock Fragmentation by Explosives. 225 1 Stephen R. Winzer et al, USA Electronic publication by Daniel Johansson 2015-06-25 after permission by Editors-in-chief Agne Rustan and Roger Holmberg

Page The Development Concept of the Integrated Electronic Detonator. Paul N. Worsey et al, USA

251

The Measuring Equipment and the Technique of Particle Velocity — at Investigation of Dynamic Rock Constitutive Equation In-situ. Wang Wu—Ling et al, China

259

Interaction between Blast Design Variables; Experimental and Modelling Studies. J.J. Dawes et al, Australia

265

Electromagnetic Velocity Gauge Measurement of Rock Mass-Motion during Blasting. Chapman Young et al, USA.

289

Discussion 5

885

Increasing Productivity through Field Control and High-Speed Photography. R. Frank Chiappetta et al, USA

301

A Method for Estimation of Fragment Size Distribution with Automatic Image Processing. Olle Carlss'on et al, Sweden

333

Instrumented Model Scale Blasting in Concrete. Gert Bjarnholt et al, Sweden

799

Discussion 6

889

Volume

1

1

Session 4. FEM AND FINITE DIFFERENCE-CODES Chairman: Gwynn Harries, vice chairman: Per—Anders Persson Numerical Simulation of Fracture and Fragmentation. L.G. Margolin et.al, USA

347

Simulation of Rock Blasting with the Shale Code. T.F. Adams et al, USA

361

Numerical Modelling of Rock Fragmentation. S. Valli'appan et al, Australia

375

Computer Simulation of Blast—Induced Vibration, Fracture and Fragmentation processes in Brittle Rocks. Peter Digby et al, Sweden

393

Computational Simulations of Dynamically induced Fracture and Fragmentation. Stuart McHugh, USA

407

Discussion 7

893

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Session 5. MATHEMATICAL MODELS'FOR BliAST AND FRAGMENTATION PREDICTIONS Chairman: L.G. Margolin, vice chairman: Roger Holmberg

Pa9e

Volume

Rock Displacement Velocity during a Bench Blast. R.F. Favreau, Canada

753

2

The modelling of Long Cylindrical Charges of Explosive. Gwynn Harries, Australia

419

2

The Kuz-Ram Model for Prediction of Fragmentation from Blasting. C.V.B. Cunningham, South Africa

439

2

Discussion 8

899

3

Computer Modelling of Fragmentation from an Array of Shotholes. C.M. Lownds, South Africa

455

2

Some Ideas on how to Improve Calculations of the Fragment Size Distribution in Bench Blasting . Hans Hjelmberg, Sweden.

469

2

Differentiated Blasting Technique for Optimum Fragmentation at Aitik Copper Mine. A case study. Gustaf Tham, Sweden

493

2

Fragmentation in Jointed Rock Material. W.L. Fourney et al, USA

505

2

Influence of Joints on Rock Blasting. A Model Scale study. D.P. Singh et al, India

533

2

Influence of Structural Geology on Controlled Blasting in Sedimentary Rocks - Case History. Goran Lande, USA

555

2

Discussions 9

903

3

Use of Comminution Theory to Predict Fragmentation of Jointed Rock Masses Subjected to Blasting. Dinis da Gama, Brazil

565

2

The influence from Primary Structure on Fragmentation. Yang Zu Guang et al, Sweden

581

2

Experimental Investigation of Dynamic Surface Response to Explosive Loading. David C. Holloway et al, USA

605

2

Discussions 10

905

3

Session 6. INFLUENCE OF JOINT AND ROCK STRUCTURE ON FRAGMENTATION Chairman: Calvin J. Konya, vice chairman: Lennart Ottosson

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Session 7. COST ANALYSES OF THE SYSTEM OF DRILLING, BLASTING, MUCKING, CRUSHING AND TRANSPORTATION Chairman: Stephen R. Winzer, vice chairman: Ingemar Marklund

Page

Volume

Electric Shovel Performance as a Measure of Blasting Efficiency. S.R. Williamson et al, Australia

625

2

Development of a Fragmentation Monitoring System for Evaluating Open Stope Blast Performance at Mount Isa Mines. J.R.T. Grant et al, Australia

637

2

The Precision of Long Hole Drilling with Modern Machines in Mining Operations. Angelo Medda et al, Italy

665

2

Discussions 11

907

3

Sublevel Stoping in Strassa Mine. Kurt Gustafsson, Sweden

585

2

Energy Requirements of Rock Breaking in Mining Operations; Considerations and Proposals. Pier Paolo Manca et al, Italy

705

2

Accurate Bench Drilling Aids - for Better Overall Economy. Bjb'rn Karlsson, Sweden.

725

2

Sources of Error in Long Hole Drilling their Consequences and how to avoid them. Per-Erik Lindvall, Sweden

739

2

The Effect of Blasting on the Grade of Ore Crushing. S.D. Victorov, USSR

909

3

Discussions 12

912

3

915

3

Opening of the panel discussion. Roger Holmberg

915

3

Part 1. The Organization of International Blasting Research and Standardization. Moderator: Agne Rustan

917

3

Part 2. New Developments in Technique to Control Fragmentation and Their Impact on Modern Mining and Construction Engineering. Moderator: Roger Holmberg

918

3

Optimization of Open Pit Bench Blasting. Kai Nielsen, Norway

PANEL DISCUSSION

"

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Page A New Technique for Controlled Small-Scale Hydraulic Fracturing. J.J. Kolle, USA

921

Errata Sheet

937

List of Participants

939

Volume 3

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First International Symposium on ROCK FRAGMENTATION BY BLASTING Lulea, Sweden, August, 1983 WELCOME TO LULEA UNIVERSITY OF TECHNOLOGY DP Torbjorn Hedberg Vice Chancellor of the Lulea University of Technology

Ladies and gentlemen, It is my very pleasant duty to greet you all welcome here to Lulea, to our University and to this part of the country. I hope that your stay here will be pleasant and we are proud to be able to act as hosts for this first international symposium on Rock Fragmentation by Blasting. This conference is an important event for this young university. It was founded only 12 years ago, although we sometimes claim this school to be the oldest institution for higher education in engineering in this country. The first such school, a mining college, was founded in Falun in 1822. It was later moved to Stockholm and merged with what later became the Royal Institute of Technology. In 1972 the parliament took the very wise and sensible decision to move the school of mining to Lulea. The reason behind the transfer was the need felt by some at least, for a better balance between the north and the south of Sweden. The same reason lies of course behind the creation of the other schools here, Mechanical Engineering, Computer Science and Technology and others. Mining is of crucial importance for this region and will remain so for a long time. The most important mines are located in this area. The present difficulties of the mines can not be overcome without strong efforts in R&D and without good university educated engineers. What we are doing in the field is therefore a part of our long term efforts to support the economic development of the area. But we do not look upon ourselves as a university only for northern Sweden. This is not true for any field and in particular not in mining where we are the only school in Sweden. And we do not want to restrict ourselves to Sweden. On the contrary, it is our clear ambition to make Lulea into an international center for mining engineering education and research. This conference is a step in that direction. Another step is the establishment of close ties with various other mining universities in the world. In a few days we are going to sign an agreement with the South Central Institute for Mining and Metallurgy in Changsha, China and I extend my particular greeting to representatives from that school present here now. I am sure this will be of mutua'l benefit. We have also many students from abroad, both in our doctoral program, as undergraduates or within our special mining technology program. The last one attracts professional engineers from many countries all over the world, mostly from developing countries. I declare this symposium opened and I wish you all a good conference.

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iSplfernational Symposium on ROGK FRAGMENTATION BY BLASTING ..-.•• Luiea, Sweden, August,-1;©83 :

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First International Symposium on ROCK FRAGMENTATION BY BLASTING Lulea, Sweden, August, 1983 OPENING OF THE SYMPOSIUM AND INTRODUCTION Dr Per-Anders Persson Chairman of Organizing Committe Nitro Nobel AB Sweden

It is a pleasure for me to open this first International Symposium ROCK FRAGMENTATION BY BLASTING. It is sponsored and arranged jointly by

on

The Swedish Board for Technical Development (STU) The Swedish Detonic Research Foundation (SveDeFo) The Swedish Mining Research Foundation, and Lulea University of Technology (LuH) The credit for the initiative to start is due to Dr Agne Rustan, who has put in a great deal of time and devotion in getting it all together, aided and abetted by Roger Holmberg and the staff of the University. It follows on the First Australian National Symposium on Rock Fragmentation in Adelaide "1973, and national symposia, for example in USA the Society for Experimental Stress Analysis (SESA) fall meeting 1980, where rock fragmentation was discussed. Many nations arrange national meetings on blasting technique annually. The first meeting in Sweden was held 1954 and it is called "Bergsprangningskommitten", Rock Blasting Committee. In Austria an "Informationstag fur Sprengtechnik", Information day for Blasting Technique", began 1969. In 1975 The Society of Explosives Engineers in USA started annually Conferences on Explosive and Blasting Techniques. By keeping to a limited special area within the science and technology of rock blasting we were hoping to get together a very qualified audience of specialists and practical blasting engineers from the mining and construction world. Looking out over this distinguished group of 157 people from 23 countries of which so many are our good personal friends, I feel we have been greatly rewarded for our efforts. We also hoped, by this initiative, to entice within the next few years perhaps, some group of people somewhere, perhaps in Australia to organize the second International Symposium on this or another special area within Rock Blasting, so that we may get together gradually a continuous documentation of technical and scientific progress in our field. On behalf of the sponsors and organizers I wish to express the hope that you all who have travelled so far will go home, at the end of the week, satisfied that you have been part of a useful, warm, informal, and friendly meeting, having learnt something new, having shared with others some of your own knowledge, and, not least important, having found new personal friends among the fraternity of rock blasters. A special welcome to the few brave ladies who have ventured this far north and into such a man—dominated part of science. I know you will enjoy the thought that this far north you are really on top of the world.

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First International Symposium on ROCK FRAGMENTATION BY BLASTING

Lulea, Sweden, August, 1983 This is indeed far north - we like to call this area the northern cap of the world — and were it not for the friendly warm westerly winds from the Atlantic Ocean and the .Gulf stream this pant of Sweden would have an arctic climate. In fact, it sometimes has that, even in summer, and you should not be surprised to see some snow on the ground one of these mornings. Still, we call this summer, by definition, because the sun is still up most of the day— time, and far into the night. So this is the time of year we enjoy the fact that there is no ice on the waters. Therefore we have included on the program a boat trip to one of the islands out in the northern part of the Bay of Bothnia, as an opportunity for you to get together, to get to know each other better, and to talk to each other, unhindered by boring speaches and papers. This is also the season for some of our peculiar Swedish eating specialities namely the crayfish and the sour herring. Perhaps you may talk one of your Swedish fellow participants into introducing you to either of these truly amazing foods, not really considered to be food at all anywhere else in the world, thus giving you a unique bond together from shared adventures. This autumn, on October 21, is the 150th anniversary of the birth of Alfred Nobel, the man who invented the detonator and the dynamite, and thereby gave a new direction to the Swedish and international development of fragmentation by blasting. So, in formally opening this birthday celebration symposium, I would like to repeat, once again, the key words for the symposium: informal — you don't need to wear a jacket and a tie warm and friendly - just be your dear natural self useful - make a point of bringing the new participants into the discussion I now have the great pleasure to introduce you to our key note speaker Mr Ulf Langefors, author of the first engineering text—book on rock blasting: The Modern Science of Rock Blasting, well—known to most of you because of his many original contributions and publications, former head of the Nitro Nobel Detonics lab and the Swedish Detonic Research Foundation at Vinterviken, and former president of Nitro Nobel.

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First International Symposium on ROCK FRAGMENTATION BY BLASTING Lulea, Sweden, August, 1983

FRAGMENTATION - A REVIEW Disintegration of Solids by Ulf Langefors Tempera AB STOCKHOLM

ABSTRACT

In this key-note speech for the First International Symposium on Rock Fragmentation by Blasting, the author gives a broad survey of the fields of structural strength and fracturing of solids. The demands set by practical needs for fragmented rock for different purposes are reviewed briefly. The development of methods for blast design and controlled blasting is outlined, and the importance for easy fragmentation of stressing rock in tension rather than in compression is pointed out. The speech ends with a call for research into unconventional methods of rock fragmentation.

1.

MATERIAL AND STRUCTURAL STRENGTH THEORIES Shell structures

The theory and methods for predicting structural strength developed over the years concern mainly shell structures. In construction and industry, buildings, ships, automobiles, airplanes or space wehicles are all shell structures. Their structural integrity depend on the designer's skill. He must correctly predict the ability of thin walls, membranes and struts to support their own weight and the external forces, and he has to choose'materials of appropriate strength.

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First International Symposium on ROCK FRAGMENTATION BY BLASTING

Lulea, Sweden, August, 1983

The finite element methods (FEM) developed by Borje Langefors and others are powerful tools for dealing with this kind of structures. These techniques have reached a level of great accuracy and refinement, thanks to the fact that one- and twodimensional approximations are easy to make and quite accurately describe the response of thin walls. Volume design and mass structures In rock design we face a different set of problems. A rock mass is a truly three dimensional structure, and often quite a complicated one. The FEM methods can be used wherever the problem has a two-dimensional nature, such as the rock stresses around a long tunnel or a tall shaft. Applications to three dimensions have been made for cases where rotational symmetry makes it possible to transform the mathematical treatment to a two-dimensional version as has been done by Bengt Akesson and others. For calculating the strength of rock caverns of an arbitrary shape a successive application of three-dimensional FEM and other iterative methods is being developed. However even present-day large capacity computers become very small when we try to introduce the rock structure around a three-dimensional cavern. Our skill is needed to simplify the problem by selecting the critical few fissures for the computer to work with. In the context of this symposium, the dynamic stress field in the rock mass surrounding a detonating explosive charge in a drillhole is an even more complicated problem where time is a fourth dimension to take into consideration. Even so, we have a surprisingly good grasp of what goes on there. The problem has been attacked from several different angles, by high speed photography where the rock is replaced by transparent plexiglass, by finite difference calculations where the rock is regarded as a compressible and deformable solid but homogeneous medium, and by such approaches as Cundall has made with his block method, where the strength and compliance of the rock fissures are taken into account but the rock blocks themselves are regarded as rigid and incompressible. 2.

THE PRACTICE IN EXCAVATING ROCK

Rock excavation is done for one of two major purposes. Either we need the excavated material to use as an ore or a mineral or for material needed in construction. Or else we are making constructions in and by the rock. Water power stations, harbours, water and drainage projects, air fields, road constructions, storage facilities are some examples. Producing fragmented rock In excavation for mining or road constructional purposes the need is generally to produce small enough debris that is easy to load and easy to crush. Sometimes, as in dam construction or when building a wave breaker it is necessary to produce quantities of large and regularly shaped boulders. Even where the main purpose of excavation is to create an empty space, such as a tunnel or an underground machine hall, the fragment size is important because it influences the speed of loading or mucking and the capacity of the transport equipment. In all these cases the degree of fragmentation influences the economy of the excavation job. Controlling fragmentation is here an important art to learn. The quantity of explosive and its distribution within the rock mass is one. The rock structure is another important factor influencing the fragment size distribution. Electronic publication by Daniel Johansson 2015-06-25 after permission by Editors-in-chief Agne Rustan and Roger Holmberg 820

First International Symposium on ROCK FRAGMENTATION BY BLASTING Lulea, Sweden, August, 1983

Remaining rock design The use of explosives as a tool to remove rock requires controlled blasting to minimize damage to the remaining rock walls and neighbouring structures. In present-day open pit mining with shothole diameters in the range 250 - 500 mm (10 to 20") each shothole may contain tons of explosive and the whole blast may involve the detonation of 200 500 tons of explosive. In underground mining large shothole diameters in the range 150 to 200 mm are increasingly being used. In tunneling larger diameter (50 to 100 mm ) and long (3 - 6 m) shotholes are also common. The development in all these areas towards larger blasts gives great savings in the cost of excavation, but also makes greater demands on methods to avoid damage. In open pit mining, the stability of the pit slopes and the corresponding slope angles influence the economy and safety of the operation. Methods are being developed to produce steeper slopes by controlled blasting that leaves the remaining rock strong enough for the increased stresses that result. Even steepening the slope by one degree may save a tremendous amount of waste rock removal in a deep and large open pit mine or road cutting. 3.

THE DEVELOPMENT OF METHODS FOR BLAST DESIGN AND CONTROLLED BLASTING

Background From Viking times into our days iron and steel have been the mainstay of Swedish economy and industry. The iron nodules on the bottom of our lakes were used up long before the 16th century. The many small iron ore mines in south and central Sweden that gave support to our great Baltic empire and our warrior kings in the 17th and 18th centuries are most of them closed down, but we still have the world's largest underground iron ore mine in operation in Kiruna and Malmberget, and Lulea, where we are convened today, is the site of one of Europe's great modern steel works. The tradition from so many years of rock and iron ore excavation lives on. Swedish miners and blasting crews are proud and independent men with a positive interest in improements an'd new methods, and from Christopher Polhem's great inventions in mining technology in the 17th century onwards Swedish mining and construction engineers have been eager to try out anything new that may bring about speed and economy in the operation. The methods of underground excavation in mining were taken over and quickly developed further in our century during the great era of hydroelectric power plant building along our northern rivers. I think that Sweden has been among the pioneers in building underground hydroelectric power plants with machine halls completely underground. The first was in Mockfjard in 1911. It was modernized in the 1950-s and is still in use. During this century also came the great developments of tungsten carbide tipped drill steels, new kinds of nitroglycerine and nitroglycerine-free explosives and waterbased explosives. These have taken the place of Nobel's original dynamites. Electric and non-electric short interval delay detonation, mechanical equipment for pneumatic or pump loading of explosives and many other tools that are part of our present day rapid excavation techniques have also been developed after the war. All these developments were borne out of this eagerness to try out and experiment with new techniques and to have a free and open exchange of results that has been and still is so characteristic of Swedish industry at its best. Out of this work grew several companies that are now assisting, on a world wide scale, industrial and developing countries to find even better methods for rock excavation, such as Sandvik and Fagersta, Atlas Copco and Nitro Nobel, the Swedish Water Power Board, Skanska and JCC, Boliden and LKAB, and a host of consulting companies.

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First International Symposium on ROCK FRAGMENTATION BY BLASTING Lulea, Sweden, August, 1983

The Nitro Nobel Detonics lab at Vinterviken, the site of Alfred Nobel's first factory, has played a certain role in this development of modern technology. Charge calculations The first step in transforming the art of rock blasting into a branch of engeneering, the modern technique of rock blasting, was to find a general formula to describe the interrelationship between charge weight and the size and geometry of the rock mass and the separation of drillholes. In its simple form, the equation

.(1)

Q = a£ V 2 + 33 V V 3 + 34 V4.

has proved a very useful tool in blast design. V is the thickness of rock to be broken loose in front of the charge of weight Q, and 32, 33, and 34 are constants. Equation1 (1) was coupled with expressions for correction for different charge geometries and charge distributions such as concentrsted or extended charges, and different degrees of fixation, by which we meant the greather or lesser accessibility of free surfaces for the broken rock to move into the surrounding free space.

(0

100 m Bufdtrt, V

Figure 1. Chsrge in kg/m-' in conformal scaling with different swell component 34. Model scale experiments Plexiglass model scsle experiments proved to be a useful sid in thinking sbout the mechanisms of blasting. From these, we began to understand the importance of the ratio between burden and spacing of drillholes in determining the size of boulders and the degree of damsge to the remaning rock. Smooth blasting and presplittinq The ideas born when looking at the small plexiglass blocks were tested in real rock, and it was found that virtually undsmaged rock walls with neat rows of split-in-half drillholes clearly visible could be produced by very minute extended specially developed Gurit charges plsced in holes with a spacing to burden ratio 0.8, using a

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First International Symposium on ROCK FRAGMENTATION BY BLASTING Lulea, Sweden, August, 1983

charge weight as low 120 grams per meter of 37 mm drillhole. Similar results were obtained by pre-splitting, where the crack between holes was formed before the rest of the blast was fired. Ground vibration measurements and control The development of short interval delay detonators and the techniques of smooth blasting made it possible to bring rock blasting right inside downtown Stockholm and other built-up areas. More and more refined instruments to record ground vibrations were developed as the need arose to check the result of decreasing the weight of charge detonated at each inerval time. Based on our own and other people's measurements of ground vibrations, the charge level Q/R3/2 (which is identical to the inverse of the reduced distance R/Q 2/3) was found to be an important damage parameter. Diagrams of the relation between charge weight and distance were produced with the charge level as a parameter, as our experience in avoiding building damage grew. We realized the possibility of utilizing the random scatter of delay times of detonators of the same delay interval number which forestalled the present-day sofisticated computer methods of delay time control to minimize vibration damage. Fragmentation Out of the plexiglass model scale blasting experiments grew also the hope of finding a simple relationship between the size of fragment or boulder size and the charge weight or burden. The resulting graph was based on a series of large blasts of medium size hole diameter in rock. It was later verified and adjusted as results of large diameter drillhole blasting became available. Size of ths bouldtrs L

07 kg/m 3 08 Sptcific ctiargt>